The present invention relates to an electronic musical keyboard instrument, and in particular to such an instrument wherein a programmable microcomputer interfaces between the keyboard and a system of capture tone generators.
Earlier electronic musical keyboard instruments, such as electronic organs, employed discrete keyers, which were individual circuits connected between the tone generator and the output circuitry and having a control input on which a keying envelope appears when the key corresponding to that keyer is depressed. Although discrete keyer arrangements permit a very large number of tones to be simultaneously played, they are quite costly due to the large number of keyers which must be provided. For example, for a typical sixty-one note manual having the usual number of footages, a total of ninety-six different keyers are necessary for each rank, and the ranks must be duplicated for brass and percussion.
With the advent of large scale integration techniques, a large number of keyers can be incorporated into a single chip thereby reducing the cost of the keyers and facilitating their incorporation into existing electronic organ circuitry. Keyers of this type still have the drawback that a given keyer is dedicated to a certain tone thereby rendering the system somewhat inflexible, and since the keyers are an integral part of major redesign of the chip.
Since there are only a small number of keys, generally twelve or less, which can be played at any one time, the vast majority of the keyers in a discrete system are idle at any one time so that the system has a great deal of redundancy built into it. Many years ago, it was recognized that a single keyer could be controlled to produce a wide variety of tones, and if enough of these tone generators are provided, then normal polyphonic playing can be accomplished. In order to control the individual tone generators to produce the desired tone, however, it is necessary to provide an interface between the keyboard which produces the control voltages, either as separate DC signals or as a time division multiplexed signal, and the tone generator units. Since the tone generators are capable of being assigned to more than one key, it is necessary to maintain a tally of which tone generators are assigned, and in some cases, even to which key they are assigned. This enables newly depressed keys to be assigned to available tone generators and to make tone generators available as soon as they are released by lifting the keys to which they were previously assigned. Tone generator systems of this type have been used for some time, and have met with varying degrees of success.